OK, there's a couple of things going on here.

First, when historians teach, they sometimes feel the need to correct common misconceptions. So, for example, they will make a big deal out of the fact that every educated person in Europe already knew the world was round in 1492, or they will go out of their way to point out that the young George Washington never chopped down a cherry tree (a story made up by Parson Weems in the early 1800s).

In the US in the 19th and early 20th centuries, there tended to be a lot of emphasis on the importance of the colonial militias. Everyone has heard of the "Minutemen," and one might also think, for example, of the famous poem, "Paul Revere's Ride," which contains the following verse [emphasis added]:

"You know the rest. In the books you have read, / How the British Regulars fired and fled, — / How the farmers gave them ball for ball, / From behind each fence and farm-yard wall, / Chasing the red-coats down the lane, / Then crossing the fields to emerge again / Under the trees at the turn of the road, / And only pausing to fire and load."

Things like this gave rise to a common fairy-tale version of the Revolution where the war basically consisted of British soldiers marching in bright red coats, while American farmers took them out from behind trees. Who needs an army, anyway?

Well . . . the Americans did. And they knew that right from the start, which is why the Second Continental Congress organized the Continental Army in June 1775, just two months after the fighting began. The Continental Army bore the brunt of the fighting, and so it tends to irritate historians when popular versions of history ignore the army (and its long years of fighting) in favor of the Massachusetts farmers immortalized in the poem.

Unfortunately, the desire to say, "No, really! The militias didn't fight the war alone!" can sometimes become "The militias didn't do a thing!" It is particularly easy to go down this road when we have vivid quotes from Washington himself, who spent the entire war irritated beyond belief at the militia, whom he regarded as undisciplined and unreliable. Consider this excerpt from a letter Washington wrote to John Hancock in September 1776:

"To place any dependance upon Militia, is, assuredly, resting upon a broken staff. Men just dragged from the tender Scenes of domestick life—unaccustomed to the din of Arms—totally unacquainted with every kind of Military skill, which being followed by a want of Confidence in themselves when opposed to Troops regularly traind—disciplined, and appointed—superior in knowledge, & superior in Arms, makes them timid, and ready to fly from their own Shadows. Besides, the sudden change in their manner of living (particularly in the lodging) brings on sickness in many; impatience in all; & such an unconquerable desire of returning to their respective homes that it not only produces shameful, & scandalous Desertions among themselves, but infuses the like spirit in others."

But this doesn't mean that the local militias were useless! They most certainly were not. The militia had some noteworthy moments. In particular, the very first battles of the war (Lexington and Concord) featured local farmers decisively beating unprepared British soldiers. Later in the war, militias played a significant role at Saratoga (a true turning point) and elsewhere.

The thing is, that Washington was frustrated because he wished that the militias would behave like professional soldiers -- but that wasn't why they existed, and it never had been. Militias in colonial America were a town-based defense system. They typically had fairly rudimentary training, elected their own officers, and didn't expect to fight for long periods of time. They tended to be most effective when fighting short-term engagements close to home. They did not carry the entire war (as older myths might have it), but they certainly bore some of the fighting, and it is not fair to read Washington's frustration with them as unalloyed truth.

Washington's letter to Hancock can be found at https://founders.archives.gov/documents/Washington/03-06-02-0305